JPH0698731B2 - Polyolefin coated steel - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polyolefin-coated steel material, and particularly when used in a high-temperature environment, a reduction in water-resistant adhesion between the coating and the steel material and cathode peel resistance. The present invention relates to a polyolefin-coated steel material in which the

(Prior Art) Since a polyolefin-coated steel material has excellent long-term corrosion resistance, it is used for corrosion protection of steel pipes, iron sheet piles, and the like. In pipelines for oil, natural gas, etc., polyolefin-coated steel pipes have been increasing due to their anticorrosive properties. Also,
In recent years, due to measures such as heating heavy oil to lower the viscosity and transporting it in order to improve the transportation of heavy oil, it is an important issue to improve the performance in the usage environment exceeding 60 ° C due to the temperature of the product being piped. Has become. Examples of the performance of the chromate treatment agent required for the polyolefin-coated steel material used in a high temperature environment include improvement in cathode peel resistance and prevention of decrease in adhesion.

As disclosed in JP-A 1-280545, the inventors of the present invention have performed a treatment with a chromate treatment agent containing phosphoric acid and silica fine particles on the surface of a steel pipe, so that the use environment exceeds 60 ° C. A method for improving the cathode peel resistance in the above is provided. Further, as to the prevention of the decrease in adhesion, JP-A-62-48
No. 543 proposes a method for producing a composite laminated steel sheet using a chromate treatment agent to which phosphoric acid and a silane coupling agent are added in order to strengthen the adhesive force between the steel sheet and the resin.

(Problems to be solved by the invention) In the chromate-treated polyolefin-coated steel material shown in JP-A 1-280545, high-temperature cathode peel resistance up to 80 ° C is good, but when immersed in hot water, resin- Adhesion between steel materials decreases. Further, the chromate treating agent containing phosphoric acid and a silane coupling agent proposed in JP-A-62-48543 has a large cathode releasability at high temperatures. The present invention provides a polyolefin-coated steel material which is improved in the chromate treatment agent proposed in Japanese Patent Laid-Open No. 1-280545, in addition to high-temperature cathode peeling resistance, and also has excellent adhesion between coating and steel materials after hot water immersion. To do.

(Means for Solving the Problems) The present invention has been earnestly studied to improve the chromate treating agent in the coating constitution disclosed in JP-A 1-280545 in order to solve the above problems. That is, on the surface of the steel material, a mixed aqueous solution of phosphoric acid and chromic anhydride is partially reduced with a polymer reducing agent, and a chromate treatment agent comprising a mixture of silica fine particles and a water-soluble silane coupling agent is applied. After baking, a primer, a modified polyolefin adhesive, and a coating of polyolefin are laminated in order to obtain a polyolefin-coated steel material that has excellent cathode peel resistance at high temperature and adhesion after hot water immersion. The inventors have found the present invention and have reached the present invention. This polyolefin-coated steel material is shown in FIG. In FIG. 1, a chromate treatment agent layer 4 containing phosphoric acid, silica-based fine particles and a water-soluble silane coupling agent on the surface of a steel material 5, a primer layer 3 made of a thermosetting epoxy resin or the like, a modified polyolefin adhesive layer 2 The present invention relates to a polyolefin-coated steel material having excellent cathode peeling resistance at high temperatures and excellent coating-steel material adhesion after immersion in hot water, which is characterized by sequentially laminating a polyolefin coating or a cross-linked polyolefin coating 1.

Hereinafter, the present invention will be described in detail.

The steel material used in the present invention is carbon steel or alloy steel such as stainless steel and titanium alloy steel. Further, on the surface of carbon steel, stainless steel, copper, aluminum, titanium, aluminum-magnesium alloy, nickel-chromium-iron alloy, nickel-molybdenum alloy, nickel-molybdenum-chromium-tungsten alloy, titanium-palladium alloy. It may be a steel material in which metals such as alloys and titanium-aluminum-panadium alloys are laminated. In addition, zinc, aluminum, nickel, copper, etc. plating on the surface of carbon steel, alloy plating of zinc-iron, zinc-aluminum, zinc-nickel, zinc-nickel-cobalt, etc., or silica plating on these plating / alloy plating Alternatively, it may be a steel material that has been subjected to dispersion plating in which fine particles of an inorganic substance such as titanium oxide are dispersed.

Next, the chromate treating agent used in the present invention will be described.

The chromate treating agent used in the present invention is an aqueous solution of phosphoric acid and chromic anhydride (CrO ₃ ) dissolved in distilled water is partially reduced with an organic reducing agent, and phosphoric acid, hexavalent chromium ions and 3 Valent chromium ions are mixed, and silica-based fine particles and a water-soluble silane coupling agent are mixed,
If necessary, a part of phosphoric acid can be replaced with condensed phosphoric acid such as pyrophosphoric acid and tripolyphosphoric acid.

Examples of organic reducing agents used for the partial reduction of chromium from hexavalent to trivalent include alcohols such as methyl alcohol and ethyl alcohol, alkylolamines such as diethanolamine and triethanolamine, saturation of formic acid, acetic acid and oxalic acid. Carboxylic acid, aromatic polyhydric alcohols such as pyrogallol, succinic acid, monomolecular reducing agents such as unsaturated carboxylic acids such as adipic acid, or starches such as wheat starch and corn starch, polymeric reducing agents such as polyvinyl alcohol Can be used. Coating after hot water immersion-To improve adhesion between steel materials and high-temperature cathode peeling resistance, a polymer reducing agent, in particular, starch containing a large amount of amylopectin, for example, corn starch is partially hydrolyzed with a hydrolase such as amyloglucosidase. Obtained by catalytic hydrolysis (average molecular weight 50000-25000), or Partially saponified polyvinyl acetate having a molecular structure of and a molecular weight of 60,000-140000 is preferable.

The above dextrin and partially saponified vinyl acetate are used in the amounts necessary to maintain the desired ratio of hexavalent chromium to total chromium. The desired ratio is preferably such that the weight ratio of hexavalent chromium to total chromium is in the range of 0.25 to 0.65. Regarding this ratio, when the weight ratio of hexavalent chromium to the total chromium is less than 0.25 and exceeds 0.65, the adhesion force after immersion in hot water tends to decrease.

The weight ratio of hexavalent chromium to the total chromium is 0.25.
The amount of dextrin required to achieve the range of -0.65 is 0.09-0.45 by weight ratio to the total chromium in the chromate treatment liquid.
And the amount of partially saponified vinyl acetate is in the range of 0.10-0.58 by weight ratio to the total chromium in the chromate treatment liquid.

The phosphoric acid added to the chromate treating agent has the following effects. Since the pH of the chromate treatment solution is lowered, the reactivity between the steel material and the chromate treatment agent is enhanced, and the reduction of hexavalent chromium to trivalent chromium is increased by heating and baking, resulting in a highly insoluble chromate film. To do. Also, phosphoric acid is a hydroxyl group on the surface of silica-based fine particles,
The chromate coating is integrated by binding to free or coordinated chromium ions, making the chromate coating insoluble in hot water and peeling the coating against the generation of alkali during the cathode peel test. It is thought to be difficult to do.

The amount of phosphoric acid added is preferably such that the weight ratio of phosphate ions to total chromium is in the range of 0.2-3.0. If the amount of phosphoric acid added is less than 0.2 or more than 3.0, the adhesion after immersion in hot water tends to decrease.

Next, as the silica-based fine particles added to the chromate treatment agent, for example, Aerosil 20 manufactured by Nippon Aerosil Co., Ltd.
0, Aerosil 300, Aerosil 380, Aerosil OX50,
Nibseal L300, Nibseal 30 from Nippon Silica Industry Co., Ltd.
0A, nibseal E200, silica fine particles such as nibseal E200A, silica-alumina fine particles such as Aerosil COK84, Aerosil MOX80, Aerosil MOX170 manufactured by Nippon Aerosil Co., Ltd., Snowtex O manufactured by Nissan Chemical Industries, Snowtex OL, Snowtex OS, Snowtex OML,
Cataloid SN, Cataloid SA, Cata manufactured by Catalysts & Chemicals Co., Ltd.
One or a mixture of two or more of colloidal silica such as loid S2OL and silica-alumina sol such as alumina sol 100 and alumina sol 200 manufactured by Nissan Chemical Industries, Ltd. is used.

The silica-based fine particles, when used in combination with the water-soluble silane coupling agent described later, have a remarkable effect on insolubilizing the chromate film in hot water or alkaline aqueous solution. The addition amount of the silica-based fine particles is preferably such that the weight ratio of the silica-based fine particles to the total chromium in the chromate treatment liquid is in the range of 0.5-3.5. If the amount of the silica-based fine particles added is less than 0.5 or more than 3.5, the adhesion after immersion in hot water tends to decrease.

Next, as the silane coupling agent added to the chromate treatment agent, γ-anilinopropyltrimethoxysilane, n-butylaminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropyltrimethoxysilane, A water-soluble silane coupling agent such as γ-glycidoxypropyltrimethoxysilane and β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane is used.

Or more water-soluble silane coupling agent is highly reactive methoxy groups in an aqueous solution (Si-OCH ₃₎ is hydrolyzed, silanol groups (Si-OH) is generated. The generated silanol groups react with chromium ions, phosphate ions, polymer reducing agents, or hydroxyl groups on the surface of the silica-based fine particles, whereby the insolubility of the chromate film in hot water is significantly improved. Further, since methyl alcohol produced by hydrolysis of the methoxy group is a reducing agent, it accelerates the reduction of water-soluble hexavalent chromium to insoluble trivalent chromium during heating and baking, thereby making the chromate film more insoluble. further,
Regarding the adhesion between the chromate film and the primer layer, since the water-soluble silane coupling agent has an amino group or an epoxy group, these organic functional groups easily bond with the amino group and epoxy group of the primer, and the chromate film and the primer layer It has a remarkable effect in improving the adhesion of the layer. The amount of the water-soluble silane coupling agent added is preferably in the range of 0.15-3.0 in terms of weight ratio to the total chromium in the chromate treatment liquid. If the amount of the water-soluble silane coupling agent added is less than 0.15 or more than 3.0, the adhesive force after immersion in hot water is likely to decrease.

Before application of the chromate treatment agent, if there is scale, oil, etc. on the surface of the steel material, alkali degreasing, pickling, sand blasting, grid blasting, shot blasting, etc. must be performed to remove surface deposits. There is. As the baking temperature of the chromate treatment agent after coating,
50-300 ° C is suitable. If the surface temperature of the steel material is less than 50 ° C, dehydration in the chromate treatment agent layer and reduction of chromium are likely to be insufficient. Above 300 ° C, decomposition of the chromate treatment agent occurs. Further, the amount of the chromate treatment agent deposited is preferably ²⁰ to 900 mg / m ² in terms of total chromium weight. If it is less than 20 mg / m ² , the effect of chromate treatment is not exerted, and if it exceeds 900 mg / m ² , a strong coating film is not formed and the adhesion is lowered.

Next, the primer used in the present invention will be described.

The primer used in the present invention contains an epoxy resin, a curing agent and an inorganic pigment as main components. As an epoxy resin,
Diglycidyl ethers of bisphenol A, AD and F, or phenol novolac type glycidyl ether are used alone or in combination. As the curing agent, an alicyclic modified amine, an aliphatic amine, a dicyandiamide-based curing agent, an imidazole-based curing agent, or the like is used. Further, as the inorganic pigment, silica, titanium oxide, wollastonite, mica, chromium oxide or the like is appropriately used. Also,
In order to improve the wettability with the resin, the surface of the above pigment may be subjected to a chemical treatment such as aluminum-silica treatment, silane coupling treatment and phosphate treatment.

Next, the modified polyolefin adhesive used in the present invention will be described.

The modified polyolefin adhesive used in the present invention, polyethylene, polypropylene, known polyolefin such as nylon, and known polyolefin copolymer resin, maleic acid, acrylic acid, unsaturated carboxylic acid such as methacrylic acid, or Modified with the acid anhydride,
Alternatively, it is a conventionally known modified polyolefin such as a product obtained by appropriately diluting the modified product with a polyolefin resin.

Next, the polyolefin coating or crosslinked polyolefin coating used in the present invention will be described.

The polyolefin coating used in the present invention means a conventionally known polyolefin such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene or nylon as a main component, and ethylene-propylene block or random copolymer. Polymer,
It is a resin containing a known polyolefin copolymer such as a polyamide-propylene block or a random copolymer.
The cross-linked polyolefin coating is mainly composed of cross-linked polyolefin obtained by subjecting the above-mentioned polyolefin to electron beam irradiation or the like to perform cross-linking. As other components, a pigment, a filling reinforcing agent, etc. can be added. As the pigment, silica, silica-alumina, rutile type titanium oxide, glass,
Mica, iron oxide red, zirconium silicate, magnesium silicate, talc, barium sulfate, alumina, zinc chromate, strontium chromate, cinnamide lead, phosphite, aluminum phosphate, calcium phosphate, silicomolybdic acid, silicotungstic acid, phosphomolybdenum General commercially available pigments such as zinc acid, and cadmium yellow, polyazo yellow, quinophthalone yellow, isoindolinone yellow, quinacridone yellow, bengara red, polyazo brown, azo lake yellow, perylene red, phthalocyanine when aesthetics are required. It is also possible to add color pigments such as blue, phthalocyanine green, red iron oxide, cobalt aluminate, aniline black, carbon black, ultramarine blue, and fine aluminum powder. That. Filling strengthening agents include glass, slag, silicon carbide, carbon, boron, boron nitride, inorganic fiber filler of alumina degree, nylon,
Organic fillers such as polyester, vinylon, aramid, and Kepler.

(Examples) Example-1 and Comparative Examples In order to specifically explain the present invention, the chromate-treating agent A- according to the present invention using various silane coupling agents will be described below.
As a comparison with the example using E, a comparative example using a chromate treating agent F-1 corresponding to JP-A 1-280545 and JP-A 62-48543 will be given.

<Example of Preparation of Chromate Treatment Liquid AE of Example> As the chromate treatment liquid AE of Example, as chromate stock solution, chromic anhydride 38.46 g and phosphoric acid 30.95 g were distilled water.
2.56 g of dextrin was added to the solution dissolved in 428.03 g, and the mixture was heated and stirred to reduce chromic acid. After cooling, 400 g of an aqueous solution containing 10% by weight of silica-based fine particles was added to this liquid and stirred. Aerosil 200 manufactured by Nippon Aerosil Co., Ltd. was used as the silica-based fine particles. Separately from this solution, an aqueous solution containing 20% by weight of the water-soluble silane coupling agent AE was manufactured by a company and mixed with the above-mentioned chromate stock solution at a weight ratio of 9: 1 for use. At this time, the weight ratio of hexavalent chromium to total chromium in the solution was 0.60, and the weight ratio of phosphoric acid to total chromium was
1.5, the weight ratio of silica-based fine particles to total chromium is 2.0,
Weight ratio of silane coupling agent to total chromium is 1.0
Met.

<Compounding Example of Chromate Treatment Liquid F of Comparative Example> As a chromate treatment liquid F of Comparative Example corresponding to JP-A 1-280545, 38.46 g of chromic anhydride and 30.95 g of phosphoric acid were dissolved in 528.03 g of distilled water. 2.56 g of dextrin was added to and heated and stirred to reduce chromic acid. After cooling, 400 g of an aqueous solution containing 10% by weight of Aerosil 200 was added to this liquid and stirred to prepare a treatment liquid. At this time, the ratio of hexavalent chromium to total chromium after reduction was 0.60, the weight ratio of phosphoric acid to total chromium was 1.5, and the weight ratio of silica-based fine particles to total chromium was 2.0.

<Preparation Example of Chromate Treatment Liquid G of Comparative Example> As a chromate treatment liquid G of Comparative Example corresponding to JP-A 1-280545, 38.46 g of chromic anhydride and 30.95 g of phosphoric acid were dissolved in 477.72 g of distilled water. To this was added 52.87 g of a 5% by weight aqueous solution of partially saponified polyvinyl acetate (saponification degree: 87%), and the mixture was heated and stirred for partial reduction. After cooling, to this solution, 400 g of an aqueous solution containing 10% by weight of Aerosil 200 was added and stirred,
A treatment liquid was prepared. At this time, the ratio of hexavalent chromium to total chromium after reduction was 0.60, the weight ratio of phosphoric acid to total chromium was 1.5, and the weight ratio of silica-based fine particles to total chromium was 2.0.

<Preparation Example of Chromate Treatment Liquid H of Comparative Example> As the chromate treatment liquid H of Comparative Example corresponding to JP-A-62-48543, chromic anhydride 38.46 g and phosphoric acid 10.32 g were dissolved in distilled water 848.66 g. 2.56 g of dextrin was added to the mixture, and the mixture was heated and stirred to reduce chromic acid. 20 to this
100 g of a wt% γ-aminopropyltriethoxysilane aqueous solution was added. At this time, the ratio of hexavalent chromium to the total chromium after reduction was 0.60, the weight ratio of phosphoric acid to the total chromium was 0.5, and the weight ratio of the silane coupling agent to the total chromium was 1.0.

<Compounding Example of Chromate Treatment Liquid I of Comparative Example> As a chromate treatment liquid I of Comparative Example corresponding to JP-A-62-48543, chromic anhydride 38.46 g was distilled water 620.24 g.
Dextrin (1.60 g) was added to the solution dissolved in, and the mixture was heated and stirred to reduce chromic acid. 0.1% by weight of 2
-Acryloyloxy acid phosphate aqueous solution 330.
0 g and 6.7 g of 10 wt% γ-glycidoxypropyltrimethoxysilane aqueous solution were added. At this time, the ratio of hexavalent chromium to the total chromium after reduction was 0.75. The composition of the liquid is shown below.

CrO ₃ : 38.46g / kg 2-acryloyloxy acid phosphate: 0.33g / kg γ-glycidoxypropyltrimethoxysilane: 0.67g / kg Cr ³⁺ / Cr ⁶⁺ = 0.33 As a manufacturing method for polyolefin coated steel Is a steel plate (9 x
(150 × 300 mm) is grid blasted, and the chromate treatment agent mixed on the surface is used as the chromium adhesion amount of 41
0-440 mg / m ² roll was applied, dried and then heated and baked at 200 ° C. After cooling the steel sheet to room temperature, apply the primer with a spray coater to a film thickness of 50 μm, then heat to a surface temperature of 220 ° C. to cure and then modify the modified polyethylene adhesive to a film thickness of 200 μm. Applied. After this, 3.0mm extruded by T-die
After applying a thick polyolefin coating under pressure, it was cooled to produce a polyolefin-coated steel material. Hot water immersion test (test temperature: 100 ° C, immersion time: 6
Adhesion measurement after 000 hours (measurement temperature: room temperature, peeling angle: 90
Degree, peeling speed: 50mm / min., Measuring beer strength when peeling the coating) and high temperature cathode peeling test (test temperature: 80
° C, electrolyte: 3% -NaCl, voltage: 1.5 V (Cu / CuSO ₄ , standard electrode), initial holiday diameter: 3.2 mmφ, number of test days: 120 days, converted peel radius of the coating film after the test: (( X / 2) ^2- (3.2 /
2) ² ) ^1/2 mm, X is the coating peeling diameter). The results are shown in Table 1. From the results shown in Table 1, the chromate treatment liquid contains phosphoric acid, silica-based fine particles and a water-soluble silane coupling agent, and the examples of the present invention do not contain a water-soluble silane coupling agent. Comparative Example F, which corresponds to
It can be seen that, as compared with Comparative Examples H and I corresponding to JP-A No. 62-48543 which does not contain G and silica-based fine particles, remarkably excellent results are obtained.

Example-2 and Comparative Example Next, in the present invention, a water-soluble silane coupling agent,
An example in which the addition amounts of silica-based fine particles and phosphoric acid are changed will be described.

<Preparation Example-2 of Chromate Treatment Liquid> A chromate treatment liquid was prepared by the same method as in Example-1 of chromate treatment liquid, and the addition amount of the water-soluble silane coupling agent in the chromate treatment liquid was changed to A polyolefin coated steel was produced. The polyolefin-coated steel material was subjected to the above-mentioned adhesion measurement after hot water immersion and a high-temperature cathode peeling test. Results are shown in FIG.

From the results shown in FIG. 2, particularly good results are obtained when the amount of the water-soluble silane coupling agent added to the chromate treatment liquid is 0.15-3.0 by weight ratio to the total chromium. Even when the addition amount was 4.0, the result was better than when the addition amount was 0.

<Preparation Example-3 of Chromate Treatment Liquid> The chromate treatment liquid was prepared in the same manner as in Example-1 of the chromate treatment liquid, and the addition amount of the silica-based fine particles in the chromate treatment liquid was changed to obtain the above polyolefin-coated steel material. Was produced. The polyolefin-coated steel material was subjected to the above-mentioned adhesion measurement after hot water immersion and a high-temperature cathode peeling test. Results are shown in FIG.

From the results of FIG. 3, the addition amount of the silica-based fine particles in the chromate treatment liquid is 0.5-3.
In the range of 5, good results are obtained.

<Preparation Example-4 of Chromate Treatment Liquid> By the same method as in Example-1 of chromate treatment liquid, a chromate treatment liquid was prepared and the addition amount of phosphoric acid in the chromate treatment liquid was changed to obtain the above polyolefin-coated steel material. I made it. On the other hand, the adhesion measurement after the hot water immersion and the high temperature cathode peeling test were performed. Results are shown in FIG.

From the results shown in FIG. 4, good results are obtained when the amount of phosphoric acid added to the chromate treatment liquid is in the range of 0.2 to 3.0 in terms of weight ratio to the total chromium.

(Effects of the Invention) As is clear from the examples, by applying a chromate treatment excellent in hot water resistance and adhesiveness to the base,
In addition to the high-temperature cathode peeling resistance proposed in No. 280545, it has become possible to provide a polyolefin-coated steel material that has unprecedented adhesion after hot dipping.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a polyolefin-coated steel material according to the present invention, and FIG. 2 is a weight ratio of a water-soluble silane coupling agent to all chromium in a chromate treatment solution and after immersion in hot water (6000
Time) adhesion force and reduced peel radius after hot cathode peel test, Fig. 3 shows the weight ratio of silica fine particles to total chromium in chromate treatment solution and after immersion in hot water (6000 hours). And the reduced peel radius after hot cathode peeling test. Fig. 4 shows the weight ratio of phosphoric acid to total chromium in chromate treatment solution and the adhesive force after hot water immersion (6000 hours). And a reduced peel radius after the high temperature cathode peel test. 1 ... Polyolefin coating 2 ... Modified polyolefin adhesive layer 3 ... Primer layer 4 ... Chromate treatment layer 5 ... Steel

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Teruo Takamatsu 1 Kimitsu, Kimitsu-shi, Chiba Shin Nippon Steel Co., Ltd. Inside the Kimitsu Steel Works, Inc. (72) Inventor, Temporary garden Yoshihisa, Kimitsu 1, Chiba Shin Nippon Steel Shares In-house Kimitsu Works (72) Inventor Hirotada Kato 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Co., Ltd. In-house Kimitsu Works (72) Inventor Kazuyuki Oyama 2784 Okami, Hiratsuka-shi, Kanagawa Japan Parker Rising Co., Ltd. (72) Inventor Mitsuru Nakamura 2784 Okami, Hiratsuka City, Kanagawa Japan, Japan Percalizing Co., Ltd. (56) References JP-A-62-268636 (JP, A) JP-A-62-83478 (JP, A) Sankaihei 1 -312082 (JP, U)

Claims (1)

[Claims] 1. A heavy anticorrosion coated steel material in which a coating layer comprising a chromate treatment layer, a primer layer, a modified polyolefin adhesive layer, and a polyolefin resin layer is sequentially laminated on the entire surface or a part of the steel material. As a treating agent, a mixed solution of phosphoric acid and chromic anhydride in a weight ratio to total chromium of 0.2 to 3.0 is partially reduced with an organic reducing agent, and silica-based fine particles in a weight ratio to total chromium of 0.5 to 3.5 are formed. , Γ-anilinopropyltrimethoxysilane, n-butylaminopropylmethoxysilane, γ- (2-
Aminoethyl) aminopropyltrimethoxysilane, γ
-Glycidoxypropyltrimethoxysilane, β-
A polyolefin-coated steel material, which comprises using a mixed solution in which one or more water-soluble silane coupling agents of (3,4-epoxycyclohexyl) ethyltrimethoxysilane are added in a weight ratio of 0.15 to 3.0 with respect to total chromium.